Such display apparatuses are used when it is necessary not only to display information graphically but also to use the apparatus for input. Such a display apparatus is useful particularly when using graphical user interfaces for operating systems or application programs. In these cases, functions are activated by buttons, in which case either the buttons can be clicked on with a cursor, for example using a mouse, or else the appropriate function can be activated by touching the display apparatus directly. Such display apparatuses are often called touchscreens.
Since such display apparatuses are able to save an input unit, display apparatuses of this kind are used in preference for small portable appliances, for example “handhelds” or PDAs. Particularly in mobile operation, however, the problem arises that there is a relatively high level of ambient brightness, and reflections appear on the display apparatus which significantly impair the legibility of the display apparatus.
From cathode ray tube units, where the problem of reflection likewise arises, it is known practice, in order to avoid reflections on the screen surface, to arrange a lattice in front of the screen, this usually being a fine-meshed wire netting, and this means that although displayed information can still be easily seen by an observer, obliquely incident ambient light can no longer cause any reflections.
In touch-sensitive display apparatuses, such wire netting or a similar apparatus cannot be used, because the relatively rigid structure means that even touching it with a relatively pointed object such as a pen would result in a broad pressure area, which can result in incorrect inputs. Even when the touch-sensitive layer has a high resolution, precise work is no longer possible.
Another known possibility for avoiding disruptive reflections is to roughen the surface pointing in the direction of an observer by starting to etch it, for example. A drawback of this solution is that the scatter effect does not just affect incident ambient light, but rather likewise affects the light which individual pixels on the display layer emit and scatter, and hence the sharpness of the image is reduced.